Geographic Range

Hypoderma lineatum ranges throughout North America, from Northern Canada to Northern Mexico. It is also found in Asia, Europe, and Africa. It is only rarely encountered south of 60 degrees latitude. (Klots and Klots, 1903; Warburton, 1922)

Physical Description

Eggs are about 1 mm in length, slender, and white in color. At one end of the egg, there are small clasp-like structures that help anchor the egg to the animal hair upon which it was layed.
Cattle grub larvae are true maggots, with retractable heads and no sclerotization or legs. After hatching from the egg, it is white in color. Pigmentation darkens (from white to yellow to light brown to black) as the larva matures and grows in size. The third instar is about 25 mm long with flat tubercles, small spines, and an obvious spiracular plate for respiration.

Pupae are coarctate, meaning that they are enclosed in a puparium. Puparium are black in color with an operculum, which is pushed open when pupation is over. Pupae are completely inactive.

The adult is hairy and has a distinctive yellow-and-black striped pattern, resembling a bumblebee. Like all insects, its body is divided into a head, a thorax, and an abdomen. It has a pair of functional wings and a pair of halteres posterior to the wings. Its mouthparts are vestigial and non-functional. (Klots and Klots, 1903; Noble and Noble, 1971; Warburton, 1922)

Development

After the egg is layed, larvae hatch within one week. Larvae then burrow through the skin of the host into the subcutaneous connective tissue, to begin its first migration. It travels, from the initial site of penetration, through the connective tissue until it reaches the submucosa of the host's esophagus where it will stay and develop through the winter. As winter is ending, the larva (still a first-instar) migrates through the connective tissue from the esophagus towards the lumbar portion of the host where it will remain for one to two months. During this time, the larva molts twice and grows significantly. For respiration, the larva situates its posterior spiracular plate towards a hole that it cuts or eats through the hide of its host. The mature larva squirms its way out of the hole (warble) and drops onto the ground when it is ready to pupate. It then burrows into the ground where it will remain in its puparium for 3-6 more weeks, depending upon environmental factors such as moisture level (humidity levels greater than 10% impede the maturation process) and temperature. After the adult emerges from the puparium, it only has 3-5 days to reproduce and start the cycle all over again before dying. (Jones, 2000; Scholl, 1993; Jones, 2000; Leclercq, 1969; Reina, et al., 2000; Scholl, 1993; Warburton, 1922)

Reproduction

Adults mate within the first few days of emerging from the pupae. Little is known of the exact copulatory habits of the warble fly.

The life cycle of H. lineatum normally spans a year's time, with warbles forming most abundantly during March and April and adults normally appearing in April and May. The Hypoderma lineatum cycle tends shift one to two months earlier in southern climates.

Lifespan/Longevity

Behavior

Adult female H. lineatum are particular about the hairs that eggs are layed on. Females prefer hairs that have a larger diameter, even though hairs with a larger diameter are much more scarce in number than narrower hairs. (Jones, 2000)

Communication and Perception

Food Habits

Larvae are parasites of large mammals, primarily cattle. A first-instar larva makes its way through the subcutaneous connective tissue of its host by secreting three different digestive enzymes into the surrounding tissue, facilitating extracorporeal digestion. Nutrients are transported across the larval body wall into the hemolymph. Nutrients obtained during this stage in the life cycle are essential for the larva's significant growth. It also feeds on dead cells, pus, and other secretions that result from the immune response. This occurs within the cyst, also called a warble, that forms on the host's dorsal area due to the larva's presence.

Pupae are coarcate and inactive, meaning that they do not feed.

An adult H. lineatum does not feed during its short life span; it must rely on stored reserves for the energy needed for the process of reproduction. (Klots and Klots, 1903; Pruett, 1998)

Predation

Little is known about predators of this species.

Ecosystem Roles

Warble flies can damage large mammal populations. At first, infected animals experience severe weight loss due to the intense action of gadding, where the animal may run around wildly trying to escape the ovipositing females, and which is believed to be stimulated by the buzzing of the flies. Secondly, the holes left by larvae do not heal over, therefore leaving the animal susceptible to other infections and opening up opportunities for myiasis by another kind of fly. (Klots and Klots, 1903; Leclercq, 1969; Pruett, 1998; Reina, et al., 2000; Scholl, 1993; Warburton, 1922)

Economic Importance for Humans: Positive

It has no known positive effect.

Economic Importance for Humans: Negative

Human cases of myiasis (infections by fly larvae) caused by H. lineatum larvae are rare; when found, the site of infection is normally the in neck region. Results of infection include leg paralysis (when spinal cord is affected), blindness (due to ocular myiasis), and creeping subcutaneous myiasis.

Hypoderma lineatum causes many problems for cattle which result in economic damage for humans. There are five major consequences that result from infection. At first, cattle experience severe weight loss due to the intense action of gadding, where the cattle gallop and run around wildly trying to escape the ovipositing females, which is believed to be stimulated by the buzzing of the flies. Secondly, because of the severe weight loss and the irritation due to the migrating larvae, milk production can be reduced up to 20 percent. Thirdly, as the larvae migrate through the host's tissue, the flesh contacted by the larvae becomes discolored, takes on a jelly-like appearance, and is no longer edible. The value of the cattle carcass is severely depreciated. Fourthly, the hide's value is also depreciated because of all the breathing holes made by the larvae. Lastly, warbles do not heal over, leaving the cattle susceptible to other infections and opening up opportunities for myiasis by other kinds of flies. (Klots and Klots, 1903; Leclercq, 1969; Pruett, 1998; Reina, et al., 2000; Scholl, 1993; Warburton, 1922)

Conservation Status

Other Comments

Research is still being conducted in hopes of developing chemical controls and vaccines against H. lineatum and other similar parasites. For the time being, methods such as dips, pour-ons, water treatment of insect growth regulators, and application of insecticide-impregnated plastic strips to legs of cattle can be utilized. It is important to note that many of these treatments are limited to very strict timeframes because many of them, when used when the larvae are already in the esophagus or dorsal area, can lead to paralysis of the host animal. (Scholl, 1993)

Contributors

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal

active during the day, 2. lasting for one day.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

scrub forest

scrub forests develop in areas that experience dry seasons.

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.